Lowara GEMK Serie Instrucciones Para La Instalación Y El Uso página 83

After establishing the layout, check that the counterpressure, or loss of head exerted by the exhaust pipe does not exceed the
maximum value indicated by the manufacturer of the diesel engine. The counterpressure depends on the equivalent length (in
Italian, "lunghezza equivalente" or Le) of the pipe, which is calculated with the formula:
Where:
L = overall length of the piping, inclusive of the bends and the expansion compensators and excluding the silencers (which are
counted separately);
sum of the increase values of the bends. The increase of a bend, "Lc", depends on the internal diameter of the pipe
and the angle of the bend.
For a "typical bend" at an angle of 90° and a radius of curvature 2.5 times the internal diameter (d), the increase "Lo" is shown in
figure 3A. For all other types of bend, the increase is Lc=k, where the coefficient k varies according to the nature of the bend
(see the picture). The "Lo" is the increase in relation to the typical bend with the same internal diameter.
Equivalent elbow length table
Internal diameter d (mm)
Equivalent length Lo (m)
The counterpressure pr (mmH20) caused by the exhaust pipe is calculated with the formula:
The formula considers a burned gas density of 1.293 kg/m3. The pressure is normally in Pascal (Pa) and not in millimetres of
water, but we have chosen to use the latter in the interest of ease for the reader, who will often find the pressure (loss of head)
to be calculated in millimetres of water (1 mm H20=9.8 Pa).
Where:
 Q = flow of burned gases (m3/min.);
 D = internal diameter of the exhaust pipe (m);
 Le = Equivalent length (m);
 T = absolute temperature of the burned gases (K°) (TK=273+T°C)
The counterpressure in the silencer indicated by the manufacturer of the exhaust silencer is to be added to the counterpressure
"pr" in the piping. The total counterpressure must be less than that recommended by the manufacturer of the diesel engine.
The internal counterpressure is first calculated considering the diameter of the exhaust piping to be equal to that of the exhaust
manifold of the diesel engine. If the counterpressure is greater than that recommended by the manufacturer, you will need to
increase the internal diameter of the piping and/or modify the layout, eliminating bends whenever possible; and then recalculate
the internal counterpressure.
We have found that with equivalent lengths of the exhaust piping up to 10-15 m, it is possible to use pipes with an internal
diameter at least twice the internal diameter of the discharge manifold of the diesel engine. When the equivalent lengths are
greater, you are advised to refer to qualified personnel.
The diesel engine's exhaust counterpressure has a major effect on the power output of the engine and its
ATTENTION
thermal load. Excessive values (measured at the exhaust manifold outlet for aspirated engines and at the
turbine outlet for supercharged engines) cause:
- a reduction in the power supplied by the diesel engine.
- higher exhaust gas temperatures.
40 50 65 80
0.5 0.7 0.9 1.2

p , 0
r
100 125 150
1.7 2.2 2.8

2
L Q

e
0013

5
d T
83
200 250 300
4.0 5.4 6.7